1. Field of the Invention
The present invention relates to a measuring device such as a micrometer for measuring length and thickness of a workpiece.
2. Description of Related Art
Conventionally, as shown in FIG. 4, a micrometer 100 has an approximately U-shaped frame 101, an anvil 102 secured to one end of the frame 101 and a sleeve 110 held at the other end thereof. The sleeve 110 is composed of an inner sleeve 103 with a base end thereof being fixed to the frame 101 and an outer sleeve 105 fixed to an outer circumference of the inner sleeve 103 protruding from frame 101. A part of an inner circumference of a tip end of the inner sleeve 103 has a plurality of slotted grooves and a female screw, and a male screw portion 104A of a spindle 104 is screwed to the female screw. A tip end of the spindle 104 without the male screw portion 104A is slidably fitted to a portion of the frame 101 for the inner sleeve 103 to be fixed, and the spindle 104 is held advanceable and retractable relative to the anvil 102. One end of a thimble 106 is rotatably free-fitted to an outside of the outer sleeve 105 fitted to an outer circumference of the inner sleeve 103, and the other end of the thimble 106 is integrally connected to the spindle 104. A ratchet mechanism 107 freerunning when more than a predetermined load is applied to the spindle 104 is provided to a rear end of the spindle 104.
A main scale 108A and main scale numeral 108B are formed on an outer circumference of the outer sleeve 105 at an even pitch along axial direction. A vernier scale 109A equally dividing the circumference at fifty pitches and a vernier numeral 109B corresponding to the number of the vernier scale 109A are formed on an outer circumference of the thimble 106 in circumferential direction at an even pitch. Incidentally, the main scale 108A is formed by engraving, printing, dichroic molding, laser marking etc. The vernier scale 109A is, as shown in FIG. 5, formed on a tapered portion 106A of the thimble 106 by engraving, printing, dichroic molding, laser marking etc.
The main scale 108A on the outer sleeve 105 is composed of a base line 111, a base scale 112 at 1 mm pitch and an intermediate scale 113 in the midst of the base scale 112, where interval between the respective scales 108A shows 0.5mm displacement. Since the thimble 106 advances and retreats for one scale distance (1 mm) of the base scale 112 of the main scale 108A by two rotations thereof, the pitch of the thimble 106 becomes 0.5 mm. The vernier scale 109A provided on the thimble 106 equally divides the circumference of the thimble 106 at fifty pitches. Accordingly, one scale of the vernier scale 109A corresponds to one hundredth of one scale of the main scale 108A. In other words, one scale of the vernier scale 109A indicates displacement of 0.01 mm.
The displacement of the spindle 104 relative to the anvil 102 can be measured by the above main scale 108A, the vernier scale 109A, the main scale numeral 108B and the vernier numeral 109B. In other words, dimension of a workpiece held between the anvil 102 and the spindle 104 can be measured by the above arrangement.
In the above-described micrometer 100, the vernier numeral 109B on the thimble 106 is from 0 mm to 45 mm (ordinarily at five scale interval) and measurement value can be read directly by the vernier numeral 109B at, for instance, from 0.0 mm to 0.5 mm section. However, when the measurement is conducted in 0.5 mm to 1.0 mm section, since the indication of the vernier numeral 109B is 0 mm to 45 mm, 0.5 mm has to be added to the current read value to convert 0.5 mm to 1.0 mm. Accordingly, read error of the measurement arithmetic calculation.
Further, the scale of the micrometer 100 is read by reading coincidence point of the base line 111 on the outer circumference of the outer sleeve 105 with the vernier scale 109A of the thimble 106. At this time, since the vernier scale 109A is formed on the tapered portion 106A of the thimble 106, parallax error can be caused in measurement. In other words, on both scale surfaces of the outer sleeve 105 provided with the main scale 108A and the thimble 106 provided with vernier scale 109A, the coincidence of the scales is read with a level difference T (according to JIS standard of not more than 0.4 mm) including end surface dimension (currently 0.25 mm) intervening therebetween, thus deviating degree of coincidence according to eye position and causing read error.
An object of the present invention is to provide a measuring device capable of reducing read error.
A measuring device according to the present invention has: a spindle advanceable and retractable relative to a workpiece; a sleeve partly screwed to the spindle and having a main scale and a main scale numeral on an outer circumference thereof along axial direction; and a thimble rotatably provided on an outside of the sleeve and integrally connected to the spindle, the thimble advancing and retracting for one scale of the main scale by two rotations thereof, the measuring device is characterized in that a vernier scale for equally dividing circumference of the thimble in a plurality of times is provided to an inner circumference of the thimble and that at least a part of a material of the thimble having the vernier scale is translucent.
According to the present invention, since the vernier scale is on the inner circumference of the thimble substantially in contact with the outer circumference of the outer sleeve, the level difference can be reduced for the dimension of the end surface of the thimble, so that the parallax error can be reduced in reading the coincidence point of the base line of the main scale and the vernier scale.
A measuring device according to another aspect of the present invention includes: a spindle advanceable and retractable relative to a workpiece; a sleeve partly screwed to the spindle and having a main scale and a main scale numeral on an outer circumference thereof along axial direction; and a thimble rotatably provided on an outside of the sleeve and integrally connected to the spindle, the thimble advancing and retracting for one scale of the main scale by two rotations thereof, the measuring device being characterized in having a vernier scale for equally dividing a circumference of the thimble in a plurality of times in circumferential direction, first vernier numeral corresponding to indication of the vernier scale, and second vernier numeral equal to addition of respective value of the first vernier numeral and the value of the vernier scale of one rotation.
According to the present invention, by providing the second vernier numeral of the thimble as, for instance, when the main scale is 1 mm pitch, 55 to 95, there is no need for adding 0.5 mm to the current read value during measurement of 0.5 mm to 1.0 mm section and the second vernier numeral can be directly read, thus reducing read error.
A measuring device according to further aspect of the present invention includes: a spindle advanceable and retractable relative to a workpiece; a sleeve partly screwed to the spindle and having a main scale and a main scale numeral on an outer circumference thereof along axial direction; and a thimble rotatably provided on an outside of the sleeve and integrally connected to the spindle, the thimble advancing and retracting for one scale of the main scale by two rotations thereof, the measuring device being characterized in that a vernier scale for equally dividing circumference of the thimble in a plurality of times is provided to an inner circumference of the thimble; that an inner circumference of the thimble has a vernier scale for equally dividing a circumference of the thimble in a plurality of times in circumferential direction, and an outer circumference of the thimble has first vernier numeral corresponding to indication of the vernier scale, and second vernier numeral equal to addition of respective values of the first vernier numeral and the value of the vernier scale of one rotation; and that at least a part of a material of the thimble having the vernier scale is translucent.
According to the present invention, by providing the second vernier numeral of the thimble as, for instance, when the main scale is 1 mm pitch, 55 to 95, there is no need for adding 0.5 mm to the current read value during measurement of 0.5 mm to 1.0 mm section and the second vernier numeral can be directly read, thus reducing read error.
Further, since the vernier scale is on the inner circumference of the thimble substantially in contact with the outer circumference of the outer sleeve, the level difference can be reduced for the dimension of the end surface of the thimble, so that the parallax error can be reduced in reading the coincidence point of the base line of the main scale and the vernier scale.
In the above, the main scale may preferably have a base scale provided at 1 mm pitch and an intermediate scale provided in the midst of the base scales, the base scale and the intermediate scale having different colors.
Further, the first vernier numeral may preferably be colored correspondingly to the base scale and the second vernier numeral may preferably be colored correspondingly to the intermediate scale.
According to the above arrangement, read error of the measurer can be further reduced. In other words, since the base scale and the intermediate scale have different colors, the measurer can be definitely aware of which one of measurement unit he is at.
Further, since the color of the first and the second vernier numeral corresponds to the base scale and the intermediate scale on the main scale, the vernier numeral corresponding to the color of the scale on the main scale most adjacent to the thimble end further distinctively comes to measurer""s sense, so that the read error can be further effectively prevented by reading the corresponding vernier numeral.